EARTH SCIENCES RESEARCH JOURNAL

Earth Sci. Res. J. Vol 9, No. 1 (June 2005): 51 -66

THE ROMERAL FAULT SYSTEM: A SHEAR AND DEFORMED EXTINCT SUBDUCTION ZONE BETWEEN OCEANIC AND CONTINENTAL LITHOSPHERES IN NORTHWESTERN SOUTH AMERICA

GERMAN CHICANGANA Corporación Universitaria del Meta, Villavicencio (Colombia) E-mail: [email protected]

ABSTRACT

The Romeral Fault System (RFS) extends 1600 km from Barranquilla-Colombia to Talara city-Peru and before the Pliocene. In the Middle Eocene RFS defi ned the northwestern border of the South America plate, being originated by a triple junction rift - rift - rift occurred from lower to middle Jurassic, when the South American sector separated from Chortis, Oaxaca and Yucatan blocks. From Late Mesozoic until Early Paleocene, the Paleo Pacifi c plate converged on NW South America corner being subducted when an anomalous thick oceanic crust, represented by the Caribbean plate, was accreted extinguishing gradually from the North of Peru to the North of Colombia. The collision generated a transtensive fi eld stress in back arc region, due to the ancestral Central Cordillera rising in continental border. The RFS rocks suffered low grade metamorphism and some rocks of extinct subduction zone suffered metamorphic inversion. During Late Paleogene until Early Miocene, the convergence South America, Farallon and North America plates produced clockwise rotation in Caribbean Plate, which moved to NE producing a dextral displacement in the suture, generating big milonyte belts in the RFS rocks. With the Farallon Plate break, in the Middle Miocene, due to Galapagos triple junction activation, the Caribbean plate moved to the NNE colliding with the south of the North American plate, being trapped between South and North American plates. This caused the Costa Rica-Panama-Choco block (CRCB) collision with the NW of South America plate, deforming the north of the Northern Andes generating a change in the convergence of Nazca plate in this sector. From Late Pliocene, when convergence change fi nish, Carnegie Ridge collision in the south of NW South America confi guring the actual lithosphere geometry and the orogenic styles of the Northern Andes. Based on Petrogenetic correlations supported by interpretation of secondary sources in geology, tectonic, petrogenesis and geophysics, a model for a regional seismotectonic characterization of this zone was done. The deformed zone represents an extinct subduction zone including fore arc basin rocks with fragments of a Lower – Late Cretaceous volcanic arc and some continental fragments of South America plate. I conclude that RFS is a weak rheologic area and a lithosphere contrast between a thick oceanic and the continental crust, presenting a high seismological activity with historically great earthquakes in Colombia and Ecuador.

Key words: Romeral Fault System, Geodynamic, Caribbean Plate, Lithosphere Delamination, Seismotectonics.

RESUMEN:

El sistema de fallas de Romeral (SFR) se extiende desde Barranquilla-Colombia hasta Talara-Perú. En el Eoceno medio defi nia el borde NO de la placa Suramerica, siendo originada por la triple unión de rifts ocurrida en el Jurasico temprano a medio, cuando el sector Suramericano se separó de las placas Chortis, Oaxaca y Yucatan. De el Mezozoico tardío al Paleoceno temprano, la Paleo-placa Pacifi ca convergió sobre el NO de Sur América para ser sub- ducida cuando la placa Caribe fue acrecionada, extinguiendose gradualmente desde Perú a Colombia. La colisión generó un esfuerzo trans-extensivo en una región ante arco por el levantamiento de la Cordillera Central en el borde continental. De el Paleoceno tardío al Mioceno temprano, la convergencia de las placas Sur America, Farallon y Norte America produjo una rotación en la placa Caribe, que se movió al NE produciendo un gran esfuerzo y desplazamiento dextral en la sutura, como así lo evidencia la presencia de grandes cinturones de milonita en las rocas del SFR. En el Mioceno medio la placa Caribe se movió al NNE colisionando con la placa Sur America, quedando atrapada entre ésta y la placa Norte America. Esto causó la colisión entre la placa Costa Rica-Panamá-Chocó y el NO de Sur America, deformando la parte norte de los Andes, y cambiando la convergencia de la placa Nazca en esta área. Desde Plioceno tardío, cuando cesó el cambio de convergencia, la Cordillera Carnegie colisionó en el NO de Sur America confi gu- rando la actual geometría litosferica y estilos orogénicos del norte de los Andes. Con base en correlaciónes petrogénicas y una cuidadosa interpretación de fuentes secundarias en Geología, Tectónica, Petrogenésis y Geofísica, se hizo un modelo de caracterización sismotectonica de esta zona. La zona deformada representa una zona de subducción extinta que incluye rocas de postarco con fragmentos de un arco volcánico del Cretacico temprano-tardío y algunos fragmentos continentales de la placa de Sur America. Se concluye que el SFR es una área reologica debil y un contraste entre una corteza oceanica delgada y una corteza continental, que presenta una alta actividad sismologica con terremotos historicos fuertes en Colombia y Ecuador.

Palabras clave: Sistema de fallas Romeral, Geodinamica, Placa Caribe, Delaminación de Lithosphere , Sismotectonica.

50 Manuscript received August 2004 Paper accepted March 2005 The Romeral Fault System: A Shear And Deformed Extinct Subduction Zone Between Oceanic And Continental Lithospheres In Northwestern South America.

INTRODUCTION metamorphism in some sectors, defi ned as Quebradagrande Com- plex (Nivia et al., 1996) which limits the Cajamarca Complex at the RFS is known as a fi rst order shear zone between 0,5 and the 8° east as San Jeronimo fault, and with Arquía Complex at the west N in the western fl ank of the Cordillera Central in Colombia. This as Silvia – Pijao fault. The other is Arquía Complex composed of shear zone has three parallel or unparallel faults intersecting each igneous and sedimentary rocks with low to medium grade of meta- to other showing in general an echelon confi guration (Barrero et morphism, besides basic and ultrabasics with HP-LT rocks. al., 1969). The RFS extends from the gulf of Guayaquil in Ecuador (Risnes, 1995; Aspden et al., 1992; Litherland and Aspden, 1992), Finally at the west of the Arquía Complex limited by Cauca - until 11,5° N near to Barranquilla in the Colombian Caribbean Almaguer or Romeral Fault, volcanic rocks has present together platform (Duque, 1980). Mesozoic basic and ultrabasics complex in tectonic contact with Meso-Cenozoic marine sediment intercalations that represent the The fi rst relation of these faults with basic and ultrabasics rocks was denominated Provincia Litosferica Oceánica de la Cordillera Oc- given by Barrero et al. (1969), later Maya and González (1995), cidental (PLOCO) and Dagua Structural Complex (Nivia, 1996). organized the geologic units surrounding to the Cauca - Almaguer Here the author shows that the RFS begins from the north of La or Romeral Fault. These authors defi ne four litodemic mega units Guajira Peninsula to the northwest Peruvian Paita Bay (Fig. 1), conforms the RFS. One unit is a continental basement represented and shows a recent seismotectonic analysis of the RFS according by the Cajamarca Complex to the east of the San Jerónimo fault. to this model in Colombia. Other ones are sedimentary and volcanic rocks owning a low grade

Fig 1. Simplifi ed tectonic – stratigraphic sketch of Romeral Fault System with its localization in the South American continent (left inset). The RFS is black thick traces and others fi rst order fault thin yellow traces. This map show principal geologic unites and allochthonous terranes infl uenced in their geodynamic evolution from Triassic.

51 Germán Chicangana

PETROLOGICS AND TECTONIC ASPECTS (1999) and Etayo et al. (1986), and also in Ecuador by Noble et al. (1997) for the Amotape terrane and for Aspden et al. (1992 a) for From isotopic data of RFS fi ve thermal events of second order in Cordillera Real. this South America were shown sector in Colombia (Maya, 2001, This thermal event indicates a NE - SW extensive phase in Cor- 1992; Aspden et al., 1987) and in Ecuador (Noble et al., 1997; dillera Central axis, at La Guajira Peninsula and in the Sierra Ne- Spikings et al., 2002, 2001, 2000; Aspden et al., 1992 a and b). vada de Santa Marta. In the lithosphere of Cordillera Central and others orogenic provinces mentioned above, suffered the same FIRST THERMAL EVENT event (Fig. 2 C). In Ecuador, both the Cordillera Real and El Oro Complex in the Amotape terrane (Noble et al., 1997; Aspden et During Permian-Triassic lapse the Pangean superplume activity al., 1992 a) register the same event. The high values in the relation (Maruyama, 1994) origined the fi rst thermal event on northwest- Sr87/Sr86 with an order of 0,70877 - 0,71065 in the Metatonalita ern South American lithosphere (fi gs. 2 A and B). In Colombia of Puquí (Ordóñez and Pimentel, 2001a), estimate a source pri- the isotopic event verifi cation was given by Vinasco et al. (2003), mary old continental crust which coincide equally with the Neís of Ordóñez and Pimentel (2001 a) and Maya (2001, 1992). The pres- Puquí, confi rming a common cortical homogeneous source. These ence of Triassic (foliated or not) granitoids at La Guajira Peninsula values coincide with those showed by Aspden et al. (1992 a), with (Maya, 2001), and at Sierra Nevada de Santa Marta (Tschanz et al., the type S granitoids of the Cordillera Real. The values showed 1974), coincide in age as some presented in the Cordillera Central for εNd (248Ma) point for the Metatonalita of Puqui (Ordóñez and and characterized by foliation and dynamic metamorphism as de- Pimentel, 2001a) and the granitoids in the Amotape terrane of Ec- scribed by Vinasco et al. (2003), Maya (2001), Orrego and Paris, uador at El Oro Complex (Noble et al., 1997) coincides.

Fig. 2. Global Geodynamic panorama from west hemisphere for Upper Triassic (A) and Lower Jurassic (B). In C y D, local geodynamic view for the northwestern South American corner in same time. The presence of foliated granitoids or not, with intermediate mag- The previous affi rmations indicate that the high values in the re- mas and corresponding to this lapse is also verifi ed equally in the lation Sr87/Sr86 and the negative values of contemporary εNd, Chortis Block (Donnelly et al., 1990) and the Acatlán Complex in point out a magmatism that extends for this whole lapse, besides the Oaxaca terrane and Chiapas Massif of the Maya Block (Cen- that geochemical and isotopic data determine a petrogenetic envi- teno – García y Keppie, 1999; Molina – Garza et al., 1992; Yáñez ronment corresponding to a pre-continental rifting phase (Wilson, et al., 1991; Moran – Centeno, 1985). In Acatlán Complex the ob- 1989), originated by the infl uence of the Pangean superplume. The served granitoid is contemporary to those of South America, and continental crust relation to Chortis and Maya blocks and South presents a strong cortical contamination with positive values for America, present similar geochemical (Noble et al., 1997) and

εNd (Yánez et al., 1991), indicating a high lithosphere thinning in paleomagnetic tendencies (Molina - Garza et al., 1992), with a the Maya block, compared with the Northern Andes lithosphere, common Mesoproterozoic basement associated to Grenvillian belt during this lapse. (Kroonenberg, 2000; Yáñez et al., 1991) (Fig. 2 C). 52 The Romeral Fault System: A Shear And Deformed Extinct Subduction Zone Between Oceanic And Continental Lithospheres In Northwestern South America.

Las Aradas–Baños–Romeral shear zone postulated by Aspden et al. Ecuador, Aspden et al. (1992 a & b), give a similar classifi cation (1992 a), obey a stress mechanism generating cratonic extension for greater Jurassic batholiths of Cordillera Real. However taking of fi rst order in this sector of South America. According to these in account geodynamic considerations for this lapse that belongs authors, I indicate that the result of the triple junction rift-rift-rift for Jurassic period (Fig. 3 A), there is not clear about the origin and caused by the Pangean superplume activity in this time separated the presence from this great magmatic belt of intermediate char- Laurentia from Gondwana (Figs. 2 A and B). This phenomenon acter in northwestern Gondwanaland. It is clear that the panorama produced a magmatism corresponding to this thermal event, which for Jurassic period in this sector is an extensive fi eld stress related originated the continental border that defi ned the northwestern to rifting (Mojica and Kammer, 1995), it is common too the pres- margin of South America plate during the Early Jurassic. This bor- ence of marine and platform sedimentation accompanied by strong der defi nes the shears zone composing the RFS (Figs. 2 C and D). subaerial volcanism such in Colombia as in Ecuador (Kammer and The Guaicaramo paleo–suture zone, in this region and time is an Mojica, 1995; Aspden and Litherland, 1992; Etayo et al., 1986). exception. The same features arise at Maya block, although in this block the volcanism is not as apparent as in Northwestern South America, SECOND THERMAL EVENT on the contrary, there is showing two sectors with different evolu- tions in this lapse. To the west a subduction zone is manifested This event is indicated by Middle to Late Jurassic big batholiths and to the east extensive phases with strong marine transgressions of Colombia and Ecuador (Maya, 2001, 1992; Noble et al., 1997; where these last ones affect a large part of the Chortis block and Aspden et al., 1992 b, 1987 b; Etayo et al., 1986; Álvarez, 1983; the entirety Yucatan block during this time (Donnelly et al., 1990; Tschanz et al., 1974). This magmatic arc observed from Sierra Ne- Servais et al., 1986; Tardy et al., 1986; Moran – Centeno, 1985). vada de Santa Marta to the north until Zamora batholith in the The petrogenetic origin of the granitoids type I is not clear accord- Cordillera Condor in the southeastern Ecuador (Fig. 1). The origin ing to the geodynamic panorama presented during this period for of this arc has not been clarity defi ned. In Colombia Aspden et al. the South American northwestern corner, it could be obeys more to (1987 b) indicate that it is product of Jurassic subduction zone and a rifting phase than a subduction zone, due to the long lapse so of Álvarez (1983) classifi es several of these granitoids as type I. For this magmatism has been registered by radiometric data.

Fig. 3. Global Geodynamic panorama from west hemisphere for Upper Jurassic (A). In B local geodynamic view for the northwestern south American corner in same epoch with cross section J – J´. See text for more details

It’s possible that magmatism in this initial phase was a product of opment of a subduction zone during the lapse Late Jurassic – Low- residual effect of rifting phase that was developed progressively er Cretaceous (Fig. 4). This age is considered for this subduction from the Triassic thinning continental lithosphere and then in the zone, due to the contemporary with a possible component strike Middle Jurassic it obeyed with more security a derived magmatic slip continuing some from these shears when it was developed an arc of a subduction zone (Fig. 3B). The regional tectonic develop- region of oblique subduction during Late Jurassic. As an examples ment in this lapse shows the possible creation of big shears and of these mega shears how the Palestina Fault, the fault systems cortical shearing in normal or oblique tendency as a result of a Pericos - Mulato - Otú, Chusma – La Plata and Salinas, Sibundoi transtensive regimen originated during this rifting phase (Fig. 2). and Suárez to the east of the RFS in Colombia and faults systems On the other hand the tectono – stratigraphic panorama that is as Chingual, Cosanga and Méndez in the oriental fl ank of Cordil- shown in the RFS that is referring for Maya and González (1995) lera Real in Ecuador. indicate with their litodemics unites let see the geodynamic devel- 53 Germán Chicangana

Fig. 4. Left: Local geodynamic view for the northwestern South American corner in Aptian times and cross section LC – LC´. See text for more details. Right: Steep slab subduction zone petrogenetic simple model showing the metamorphism and transformation phases itself sensu Peacock (1993) and Hacker et al. (2003 a y b).This hypothetic model suggest petrologic analogy with Arquía Complex together with basic and ultrabasic rocks, HP - LT rocks and arc volcanic Quebradagrande Complex.

THIRD THERMAL EVENT oceanic crust that have suffered diverse grades of metamorphism, related by their space and time features with a typical subduction This event extend from end of Late Jurassic until of the Lower zone due its physical conditions (Hacker et al., 2003; Peacock, Cenomanian in Late Cretaceous along of the RFS. It’s represent by 1993, 1990). extinct subduction zone (Arquía and Quebradagrande Complexes, besides to basic and ultrabasics rocks (Álvarez, 1987 a and b) that Next to these rocks there associate belts or fragments of blue schist, accompany this tectono - stratigraphic framework). gabbros and ultrabasics rocks (Fig. 4). The same way is observed with Arquía and Quebradagrande Complexes in several sectors Correlatively with the Quebradagrande Complex (Nivia et al., like in Pacora, Pijao, Barragán and Jambaló (Maya, 2001; Álvarez, 1996; Maya and González, 1995), in their age and stratigraphic 1995). The same situation happened with the Ruma terrane rocks characteristic like the association of volcanic and sedimentary in La Guajira Peninsula and the Seville microterrane in Sierra Ne- rocks with or without metamorphism, these are the Paraukrien vada de Santa Marta (Maya, 2001; Etayo et al., 1986; Tschanz et Formation in La Guajira Peninsula, the magmatism that produce al., 1974), their petrologic associations let perceive a subduction the Riolita Golero and granitoids of contemporary age in the Si- zone. In Ecuador similar fragments presented as Peltetec Ofi olitic erra Nevada de Santa Marta and the Metabasaltos y Piroclásticas Complex in the western fl ank of the Cordillera Real and Raspas Asociadas next to the San Pablo Formation in the Campamento Metamorphic Complex in the Amotape - Tahuin terrane (Bosch terrane in Colombia (Maya, 2001; Etayo et al., 1986; Tschanz et et al., 2002; Arculus et al., 1999; Aspden and Litherland, 1992; al., 1974; Hall et al., 1972). Litherland and Aspden, 1992; Aspden et al., 1987 a).

For Ecuador this correlation is made with the Alao - Paute unit with Assuming the stratigraphic and tectonic context of RFS with Ar- Alao terrane in the western fl ank of Cordillera Real (Aspden and quía Complex and basic and ultrabasic rocks shows in Fig. 1, Ernst Litherland, 1992), and the Celica Formation to the south of Loja (1988), indicates that retrograde metamorphism that some of these terrane and in the Amotape terrane (Jaillard et al., 2002, 1999). The units present is typical for subduction zones as part of its tectonic Quebradagrande Complex has been considered that represents a history in HP - LT rocks like blueschists and eclogites, produced magmatic arc located above a subduction zone (Nivia et al., 1996). an ascent of subducted material toward to surface after detachment In the case of La Guajira Peninsula and Sierra Nevada de Santa takes place of descending slab, adding in this process mantle ma- Marta rocks, this type of confi rmations has not been made, while terial like ultrabasics rocks. These processes of exhumation obey Alao - Paute unit is very deformed (Aspden and Litherland, 1992). to changes in the convergence among the plates or to a complete The Celica Formation allows let see the development of a fore ceasing of the subduction. England and Molnar (1993), indicate arc basin which was controlled by a convergence regime (Jaillard that the heat dissipation rate for volume unit in the shearing regions et al., 2002, 1999). The spiderdiagrams shown for diverse points where rocks are exhibited with high grade of metamorphism juxta- that Quebradagrande Complex by Nivia et al. (1996) and for the posed with rocks of low grade of metamorphism, are the product volcanic rocks of the Celica Formation in Ecuador for Jaillard et of the shears stress and strain rate. For that reason the areas of high al. (2002), indicates that derived magmas of a subduction zone heating not necessarily coincide with those of more deformation. (Wilson, 1989). This situation makes diffi cult to determine how were distributed the dissipation sources of shear heating in this area when it was ac- The Arquía Complex just as it age and petrologic characteristic tive. About this, Aoya et al. (2002), estimate for these mechanisms described in the literature (Maya, 2001, 1992; Maya and González, a clockwise sense trajectory to the pressure versus temperature 1995), let see that it is igneous and sedimentary rocks associated to during a change in the convergence during a subduction develop- 54 The Romeral Fault System: A Shear And Deformed Extinct Subduction Zone Between Oceanic And Continental Lithospheres In Northwestern South America. ment zone which is mainly related to a subduction jump, interpret- fault in La Guajira Peninsula and Sierra Nevada de Santa Marta. ing for this that a rock fragment with previous metamorphism and This appreciation can be confi rmed in Ecuador at Baños – Las an equivalent thickness at the perpendicular distance between the Aradas faults (Aspden and Litherland, 1992), but not at Amotape old and the new subduction zone, must have an effect on the post terrane. collision heating, but this won’t require a special source of heat or tectonic event. This phenomenon causes the deviation of the The fundamental shear here proposed, was originated during the conditions in the temperature from the metamorphism to a low re- development of this subduction zone during this thermal event, but lation of temperature and pressure in the contemporary geotherms their present current tectonic - stratigraphic disposition obeys to along the upper limit of the subduction zone. About on this con- changes during the evolutionary course of this continental margin text, Cloos (1993) estimates that when a collision is present in a in Cenozoic times. subduction zone, ceases its development and is presented a new subduction zone with its own jump, causing a dramatically change FOURTH THERMAL EVENT over the convergence model and a movement of the plates that made origin to the fi rst subduction zone. The fourth thermal event extends from Late Cretaceous until Late Eocene (Ordóñez et al., 2001; Aspden et al., 1992 b, 1987 b). This With the above-mentioned, the tectonic – stratigraphic disposition thermal event presented in this lapse for western Colombia are along of RFS showing retrograde metamorphism phenomena being related to the thermal activity of two different lithospheres, one observed in Arquía Complex and rocks associated in the places like properly oceanic to the west and other related to the continental Pijao and Barragán in Colombia and equally in the Raspas Meta- margin, showing both two unlike geodynamics panoramas. morphic Complex in Ecuador (Maya, 2001; Mojica et al., 2001; González, 1997; Bosch et al., 2002, Gabrielle, 2002; Arculus et al., For the oceanic lithosphere located to the west of the RFS during 1999). The cause of this tectonic history in this subduction zone is Aptian - Albian was manifested in abundant extrusion of the Pacif- the increase and collision during the lapse Late Cretaceous – Early ic superplume in the Ocean Pacifi c basin, causing an exaggerated Paleogene of continental and Caribbean – Colombian Cretaceous increase of the oceanic crust in this sector of the planet (Larson, Igneous Province or Caribbean plate fragments in the western mar- 1991). This crust conforms part of the paleo - Pacifi c plate or paleo gin of South America (Aspden and McCourt, 2002; Spikings et al., - Caribbean (Mauffret and Leroy, 1997), which begins to accreted 2002, 2001; Kerr et al., 1998; Nivia, 1996; Litherland and Aspden, with the western margin of South America during Campanian in 1992; Aspden et al., 1987 a). Equally synchronous at this event Ecuador (Aspden and McCourt, 2002; Kerr et al., 2002). also manifested a basic magmatism in back arc region toward the east of RFS at Cordillera Oriental in Colombia and Oriente Basin After the Aptian - Albian event in the central Pacifi c, during the in Ecuador (Moreno et al., 2001; Barragán and Baby, 1999; Bar- lapse Cenomanian – Turonian lapse has an apparently reappear- ragán et al., 1997). This obeys in Ecuador probably to a slab roll ance of the phenomenon, indicating like a special characteristic the back derived of a ceasing of the subduction with a possible slab presence of komatiítes and picrite tuffs with a high MgO contents. break off mechanism in Early - Late Cretaceous lapse (Barragán These lavas are presented in several places of the Caribbean plate and Baby, 2004) and in the sites 803, 1185 and 1187 at the oriental fl ank of the oceanic Ontong Java plateau in the Kroenke submarine canyon In tectonic evolution during this thermal event, the fundamental which dispose among the atolls of Ontong Java and Nukumaru in shear of RFS represented by Silvia – Pijao fault that puts in the the Nauru basin (Kerr, 2003; Mahoney et al., 2001; Arculus et al., limit the Arquía and Quebradagrande Complexes in Cordillera 1999; Mamberti et al., 1999; Alvarado et al., 1997; Orrego and Central. Simarua fault in La Guajira Peninsula and Seville Lin- Espinosa, 1989; Alvarez, 1987 b). eament in Sierra Nevada of Santa Marta, Colombia, those which present some likeness in age and petrologic with the Arquía Com- The coincidence of the ages for both igneous provinces, the strong plex and the volcanic or equivalent arcs (Maya, 2001; Maya and likeness among the Cretaceous faunas of the Caribbean with the González, 1995; Tschanz et al., 1974). In Ecuador this shear is rep- Line – Nauru basin Islands (Nivia, 1989), and the similarly geo- resented by not differentiated traces of Peltetec fault that separate chemical characteristic that point out lavas of high temperature to the Unit Alao – Paute of the Ofi olitic Peltetec Complex in the related to primitive or primary magmas that are presented such as Cordillera Real, and Tahuin Dam fault located between Amotape in the Caribbean plate as in the Ontong Java plateau during Ceno- terrane and Raspas Metamorphic Complex, in Amotape Range at manian - Turonian lapse insinuates the correlation of these crusts southwestern Ecuador, and Celica fault between Amotape terrane with a common source in its origin, or a tectonic special dynamics and the Celica Formation at east fl ank of Amotape Range in north- too, that produced an extreme thinned of upper lithosphere, so that western Peru (Bosch et al., 2002; Jaillard et al., 1999; Aspden and these lavas were presented contemporarily in both igneous prov- Litherland, 1992; Aspden et al., 1987 a). San Jerónimo fault (Maya inces. It is also necessary to emphasize that these lavas are excep- and González, 1995) separates the Quebradagrande Complex of tional for the Phanerozoic and apparently they are only presented the western continental lithosphere in Colombia. Cannot be iden- in these two igneous provinces in the planet (Kerr, 2003). tifying with some equivalent trace that completes the paper of this

55 Germán Chicangana

Fig. 5. A. Global Geodynamic panorama from west hemisphere for Late Cretaceous and B. Paleocene., showing the source possible for Caribbean plate. See text for more details

Considering this it is possible to mention that during Aptian as in the other regions in both cases, because its represented a jump - Turonian lapse both conformed a single igneous province and in the subduction zone and magmatism indicates the presence of that after this lapse they get separated (Figs. 5 A and B). Such as a volcanic arc in this sector of the continental frontier (Aspden the Caribbean plate as the Ontong Java plateau showing by geo- and McCourt, 2002; Kerr et al., 2002; Reynaud et al., 1999). The physical evidences high thickness crust (Kerr, 2003; Maloney et collision in its fi rst phase produced the ascent and exhumation of al., 2001; Mauffrett and Leroy, 1997). It is possible that here it the deep geologic units of Cordillera Real generating the inversion was a single great Cretaceous igneous province, and that a triple metamorphism and shear of these rocks in Loja and Salado ter- joint produced this exceptional extrusion with lavas that represent ranes (Spikings et al., 2001). In Colombia this accretion was take a primitive magma. This triple joint would be conformed by Orien- place gradually toward north until the Middle Eocene (Fig. 6 B) tal Pacifi c ridge and possibly west extension of one ridge defi ning producing a fi rst order unconformity for this sector of the north- the triple joint rift - rift - rift that separated in Triassic - Jurassic ern Andes and Colombian Caribbean platform when accreted the North and South America. PLOCO and San Jacinto accretionary wedge (Nivia, 1996; Duque, 1984, 1980). The Caribbean plate accreted in Campanian at the western margin of the northwestern South American corner. Dynamic metamor- The oblique collision and the dextral displacement of the Carib- phism increment in shears of RFS due to the effect of this collision bean plate toward the NE in this margin during Paleogene (Figs. (Fig. 6 A). Previous to this, Amotape and the Chaucha - Guamote 6 A and B), develops an regional unconformity and produced a terranes accreted with the Ecuadorian continental margin (Jaillard gradual exhumation of the RFS rocks and in several sectors the et al., 1999; Aspden and Litherland, 1992 a). These accretions pro- milonytes belts development mainly in the faults that constitute duce decrease in the magmatism product of a developed subduction and correspond to limit between the subduction zone and the Early zone from the Late Jurassic in the continental margin (Ordóñez et - Late Cretaceous volcanic arc, represented by San Jerónimo and al., 2001; Maya, 1992; Aspden et al., 1992 b, 1987 b). Spikings et Silvia - Pijao faults of Cordillera Central in Colombia. This pro- al. (2002, 2001 and 2000), show by modeling with fi ssion tracks cess produces the metamorphism retrograde in the rocks that form in apatite, zircon and white mica for Ecuador the increment of the this shear zone producing reactivation or the development of fi rst cooling rates in the continental lithosphere, being observed a pe- order faults like Pallatanga, Pujilí, Calacalí and Peltetec in Ecuador riod of cooling for the Cordillera Real and the Amotape terrane. A (Kerr et al., 2002; Spikings et al., 2001; 2000), Cauca – Almaguer fi rst event for Maastrichtian – Paleocene lapse is coincident with fault in Cordillera Central in Colombia and Romeral Lineament in the accretion of the Pallatanga terrane in the continental margin of Colombian Caribbean platform. The accretion of the oceanic ter- Ecuador and a second event for Middle Eocene with the accretion ranes to the west of the RFS defi nes structural limits of fi rst order in this margin of the Macuchi terrane (Aspden and McCourt, 2002; like Cauca – Patía Fault zone in Colombia and San Isidro - The Kerr et al., 2002). Equally these authors show for the Cordillera Angel, Canande, Daule - Apuela, Pallatanga, Calacali, Pujuli and Occidental in Ecuador, a fall in the heating, but its not as constant Chimbo - Toachi Lineament among others in Ecuador.

56 The Romeral Fault System: A Shear And Deformed Extinct Subduction Zone Between Oceanic And Continental Lithospheres In Northwestern South America.

Fig. 6. Local geodynamic view for the northwestern South American corner in Paleocene with cross section P – P¨ (A), and Middle Eocene with cross section E – E¨ (B). See text for more details.

Cloos (1993) indicates that for the collisions in the active margins, showed under the continental margin in the Cauca - Patía basin and in the jump of a subduction zone a displacement of the magmatic in Cordilleras Central and Occidental in Colombia. The long activ- arcs is presented. In our case that is presented toward the west of ity in the time of this magmatism obeys to convergence develop- the collision area that is represented by the RFS. It was also pre- ment of Nazca plate under South American northwestern margin sented the development of a shears zones accompanied by heating from Early Miocene resulting of the Galapagos triple junction lo- as a result of a strong dextral displacement which produced the cated in this sector of the Oriental Pacifi c (Georgen and Lin, 2002; dynamic metamorphism in this collision area, as a result of a series Hey, 1998, 1977). The partition of the Farallon plate in Cocos and of the phenomena that’s conjugate a panorama of lithosphere de- Nazca plates starting from this triple junction caused that Carib- lamination (Schott et to the., 2000; Schott and Schmeling, 1998). bean plate moved with tendency ENE in contact with South Amer- Development of this panorama over the low lithosphere can pres- ican northwestern margin until getting inserted between North ent the separation or the partial disintegration of the old subducted America and South America during Neogene (Figs. 7 A - C and 8). slab. The fi nal consequence of this convergence is the accretion and col- lision in the Late Neogene of Costa Rica - Panama - Choco Block FIFTH THERMAL EVENT (CRPCB) in Colombia northwestern corner, together with accre- tion of Sinú accretionary wedge in Colombian Caribbean platform This event begins at Early Miocene in Colombia (Risnes, 1995; (Chicangana and Vargas, 2003; Chicangana et al., 2002; Duque, Maya, 1992; Aspden et al., 1987 b). This calc - alkali magmatism 1990 a and b, 1984, 1980, Escalante, 1990).

Fig. 7. Local geodynamic view for the northwestern south American corner and its cross section respectively. A. Early Miocene with cross section M – M¨. B. Late Miocene with cross section LM – LM¨. C. Early Pliocene with cross section P – P¨. Black arrows indicate cinematic tends of principal tectonic structures including RFS and cross sections to right left showing delamination lithospheric processes evolution in old slab due to subduction zone jump. See text for more details.

57 Germán Chicangana

Fig. 8. Actually local geodynamic view for the northwestern south American corner in with cross section H – H¨ also showing allochthonous terranes and geologic units accreted during late Cretaceous – Paleogene lapse to west of RFS, and black arrows point out cinematic tends of main tectonic structures of this region at present time.

The development of Neogene’s magmatism verifi ed with geo- surface. Its observed that a strong extensive régime is presented as chemical indications showing in western Colombia from Middle a result of the increment of tension of the upper lithosphere by the Miocene a strong likeness with the mantle source (Ordóñez y Pi- effect of the orogeny in the area of the collision that produced the mentel, 2001b). In Ecuador from Middle Miocene until present activation of normal faulting in back arc basin to the east of the a cooling of the lithosphere besides an ascent and exhumation of RFS during the collision of the Caribbean plate such in Colombia deep rocks has verifi ed (Spikings et al., 2002, 2001, 2000), addi- as in Ecuador. Toward fi nal of the Paleogene and Early Neogene tionally there is, a change is presented in the magmatic differentia- were originated big faults as result of a transtensive regional re- tion for Late Neogene causes a big affi nity with a mantle source gime in this sector of South America. These faults in Colombia are (Chiaradia and Fontboté, 2003). This likeness made the mantle the Santa Marta – Bucaramanga Fault (SMBF), Cesar Lineament also observed in recent basic extrusions in southwestern Colombia and Tigre fault in the northeast (Etayo et al., 1986). Toward south- (Rodríguez and González, 2003). west big shear systems reactivate in the eastern piedmont of the Cordillera Central while that the RFS developed dextral pull apart The change in the magmatic differentiation of this thermal event basins as result of the displacement to the NE of the Caribbean in Colombia and Ecuador for the Late Neogene indicates a change plate (Figs 7 A and B). under the conditions from the lithosphere at the end of this lapse. According to Schott et al. (2000) and Schott and Schmeling (1998), When the Caribbean plate trapped between North and South during a process of delamination in the ductile conditions of the America during the course of Late Miocene to the Early Plio- lower lithosphere, big shears being developed originate a separa- cene (the Fig. 7 C), a great left displacement take in FSMB that tion of subducted slab take place materials with smaller density changes place the north end of the RFS displacing the Sierra Ne- that ascends while those of more density descend in the mantle. vada of Santa Marta and La Guajira Peninsula regions toward NW This condition is in function of the age of the detachment slab and for a great distance (Boinet et al., 1981). With the collision of the the space left by this phenomenon, which is fi lled by the upward CRPCB from Late Pliocene in the northwestern Colombian corner material of the mantle. When this kind of evolution occurs in the (Figs. 7C and 8), a change is presented in the tendency of the dis- lowest lithosphere, the new disposition of the subducted slab to placement in the RFS become in left slip sense between the 4 and the west of RFS reconfi gures this astenospheric wedge generating the 7,5°, while to the south of the 4° N until the 4° S in the Gulf a thinned lithosphere. The interference of basic magmas took place of Guayas original right sense is conserved, while to the south of in several cases when they were favored with the propagation of this latitude Jubones fault presents left slip (Steimann et al., 1999; the big shears from the lowest to the superior lithosphere due to the Ego et al., 1996). regional extensive régimes that helped basic magmas emerge to the

58 The Romeral Fault System: A Shear And Deformed Extinct Subduction Zone Between Oceanic And Continental Lithospheres In Northwestern South America.

Fig. 9. Hypocentral Cross sections using 1993 – 2001 local seismological data from the National Seismological Network of Colombia (RSNC) (Ingeominas, 2001), with 1° of wide of section in these 7819 earthquakes were applied registered in more than 4 seismographic stations network. A. Flat slab between 5,5° - 7,5° N. B. Steep slab between 4,5° – 5,5 ° N. C Steep slab between 3,5° – 4,5° N. C. Steep slab between 0° – 3,5°. RFS indicate localization of Romeral Fault System zone. No vertical exaggeration.

Fig. 10. 3D hypothetic topographic view of slab subducted surface below northwestern South American corner from RSNC database.

59 Germán Chicangana

Fig. 12. Left, historical seismicity 1471 – 1991 report data SISRA (NEIC, 2000), with MS > 6,5 events only. Right, 1993 – 2001 local seismicity report by National Seismologi- cal Network of Colombia (RSNC). 1. Colombian Caribbean platform. 2. Between 3,5 - 7,5° N, and 3. Between 0 - 3,5° N. See text for more details. When the collision was completed and the Isthmus of Panama The development of the adjustment of convergence during Late emerges during the Late Pliocene (Duque, 1990 b), the Nazca plate Pliocene to Early Pleistocene lapse took place in several sectors an in this sector presents besides with the CRPCB positive buoyancy, effect tensional in big lithospheric shears that derive of the delimi- a left displacement is presented to the southeastern of Panama nation lithosphere. These big shears favored the expulsion of the (Cowan et al., 1998) and fl at subduction is observed between the basic magmatism in the southwestern of Colombia and the pres- 5,5 and the 7,5° N in Colombia (Monsalve, 1998) (Figs 9 A and ence of these basic magmas in the bodies of the Late Neogene por- 11). The limits of this accretion being faults as Uramita, Garrapa- phyry bodies in Ecuador. On the contrary, to the north of the 5,5° tas, and the Sinú lineament that toward the south is called Monteria N, observed that the magmatism was very restricted and by effect fault. of cortical thinning product of the delamination its displaces to- ward to the east, this situation produced ignimbrites and tuffs vol- Equally as a result of this collision there are strike- slip faults sys- canism activity in several sectors of the Cordillera Oriental during tem like the Ibagué fault and the reactivation of Espiritu Santo this last lapse (Garzón, 2003). His last situation seems that stays at fault that belong to the RFS (Figs. 1 and 8). Lastly the develop- the present time with the manifestation of hot springs in the Cundi ment of this accretion produces a gradually rising of the Cordillera - boyacence highlands and in the eastern fl ank of Cordillera Ori- Oriental in Colombia, estimating that the propagation of the sub- ental (Fig. 8). Also by the effect of the delamination, takes place duction of the Nazca plate to the 5,5° North and the convergence with this new collision the ascent of many relatively deep rocks of the Caribbean plate, produced the rising of this orogenic con- of the upper lithosphere as the Mesoproterozoic basement and big text as Cordillera de Merida to the west of Venezuela, by activa- igneous intrusions resultants of the Jurassic - Cretaceous arc like tion of thrusting on the Falla Frontal de la Cordillera Oriental or Antioquia batholith among others. North of the 7,5° with the ad- Guaicaramo fault in Colombia and of the Piedemonte Oriental in justment of the Caribbean plate between North America and the Venezuela. The displacement on the Caribbean plate in this last South America plates together the subduction of the Cocos plate to sector produces right displacement in Boconó fault and kinematics the SW, this plate moves along the north margin of South America tendency is observed from Cosanga fault in Ecuador (Eguez et al., that collides with the continental crust in an oblique convergence 2003) until Boconó fault in Venezuela (Audemard et al., 2000), in this sector. indicate a anticlockwise rotation of the South American plate in this lapse, situation that stays until today (Fig. 8). In this continental margin are developed in E - W sense big strike slip faults like Oca and Cuisa faults. The lateral displacement of Following the Colombia - Ecuador trench the Nazca angle slab in- Caribbean plate in this sector produces a separated development creases until the 3° N (Figs. 9 B - C and 10), where again it decreas- pull apart basin in these E - W faults. This behavior continues from es (See Fig. 9 D) until the 4° S due to the infl uence of the Carnegie northeast Colombia until northeast Venezuela (Audemard, 1996). ridge collision on this margin. On south of this latitude, again this The development of this convergence produces clockwise rota- angle is increased until the 5° S when it begins to decrease when tion of the Sierra Nevada of Santa Marta with a strong ascent in presented the fl at subduction of Nazca under the northwest of Peru this last orogen, operate as backstop the Tigre fault for produce a (Gutscher et al., 1999). Its oblique convergence of the Nazca plate symmetrical orogen. In La Guajira peninsula the displacement that and Carnegie ridge to the south produced the successive rising of took place by this effect produced a total basement emergency to the Cordillera Occidental in Colombia and the fi nal ascent of the the north of Cuisa fault and the partial emergency between Cuisa Cordillera Real in Ecuador (Spikings et al., 2002, 2001, 2000). and Oca fault. 60 The Romeral Fault System: A Shear And Deformed Extinct Subduction Zone Between Oceanic And Continental Lithospheres In Northwestern South America.

SEISMOTECTONICS America separation from a triple junction joint rift - rift - rift dur- ing the Late Triassic – Early Jurassic lapse. Then under this margin The seismicity presented for the diverse sectors along the RFS in was presented a subduction zone which was active from Middle Colombia, is the result of the convergence of these plates from - Late Jurassic until Late Cretaceous when it began to be trun- Late Pleistocene (Figs. 8, 9, 10 and 11). At Colombian platform cated by Caribbean plate by effect of it collision with northwest between the 7,5 and the 11,5° N (Fig. 11), ơ1 tend ESE take place margin of South America. From Paleogene until the present the a shallow seismicity with earthquakes ML ≤ 4,0 and an intermedi- RFS suffered the dynamic metamorphism and exhumation of its ate seismicity with earthquakes ML ≥ 5,0 (Chicangana and Vargas, deep rocks as resulting mechanism in the upper lithosphere of slab 2004). Historically earthquakes have been observed with MS ≥ separation at lower lithosphere by the effect of lithosphere delami- 6,0 for region of Sierra Nevada de Santa Marta. For this region nation development by this collision that which takes place totally an event of these characteristics with a depth hypocenter 58,3 km under this region of South America during Paleogene – Neogene in this region registered by the National Seismological Network lapse. of Colombia (RSNC) in February of 2004 (Ingeominas, 2004). These events are possibly attributed to the Oca Fault activity (Paris Also here is exposed a fi rst attempt of direct correlation of Carib- et al., 2000). The registered of local seismological data in this re- bean plate with the Ontong Java plateau considering secondary gion is unfortunately very poor due to the very low density of the sources as the bioestratigrafi c and petrogenesis, something that seismographic RSNC stations and the registration of the events Reynaud et al. (1999), has been doing with the rocks of the of is taken mainly of NEIC. Because it is not possible to fi nd stud- the Piñon terrane in Ecuador, this concepts are considering with ies of good quality on local seismic activity of this region, what a new sketch of the geodynamic that explains a lithosphere with helping to determine seismic areas and less for intermediate and the anomalous thickness in the Pacifi c’s oceanic crust that tries long – term seismic hazard prediction analysis for this region of to demonstrate the abnormal pulse of the Cretaceous Superplume Colombia. proposed by Larson (1991), as the origin of the oceanic crust that represents the Caribbean plate in present. This correlation also ex- Between the 3 and the 7,5° N (Fig. 11), a drastic change is ob- plains many of the tectonic and stratigraphic phenomena that are served in the angle of Nazca slab (Monsalve, 1998). In this sector observed in the RFS that derived mainly of the accretion and col- (Fig. 8) ơ1 is predominantly NW - SW (Chicangana et al., 2003, lision of this oceanic crust of anomalous thickness in this subduc- 2002), with prevalence of high seismic activity that is observed tion zone in northwestern South America. in Colombia trench with MW ≥ 5,0 shallow events, Pacifi c coast platform and Cordillera Occidental. Equally a great intermediate The consumption of the lithosphere in this continental margin de- seismicity associated to the subduction zone is observed where the rived from delamination and the later convergence of the plate of scale goes from 3,5 and the 5,5° N a bigger rate of events is pre- Nazca plate during the Neogene has left an area of cortical weak- sented with MW ≥ 4,0. Many of these last earthquakes in some ness (RFS) trapped between two rigid crust represented by a con- cases have produced destruction and lost human at historical times tinental to the east and an oceanic to the west. This convergence in Colombian Eje Cafetero region, as the events of November of for Late Neogene defi nes the three different stress fi elds tends in 1979 and February of 1995. In the region along RFS two dozens Colombia. The analysis of these stress fi elds and the seismological of shallow events have been presented with MS ≥ 4,5 in near 450 behavior of each one of these areas, show a rate seismicity increase years of historical data, and more recent was the earthquake MW ≈ from this shears zone to the south 3° N than to the north. Finally 6,2 in January 25 1999 that destroy Armenia city. it is observed that the change on Nazca plate slab angle, under Eje Cafetero region to western Andes (3,5° - 5,5° N) increase of Between the 0 and the 3,5° N (Fig. 11), with (Fig. 8), ơ1 predomi- the intermediate seismicity activity. This last seismogenic source nantly NE – SW (Ego et al., 1996), the subduction zone seismicity historically has been responsible for big earthquakes that have af- activity is lower than in north of the 3° N, but in the Colombian fected specially this region of Colombia. - Ecuadorian trench have happened MS ≥ 7,5 earthquakes with re- turn rate of an event of this dimension in less than 20 years for this ACKNOWLEDGEMENTS region such in Colombia as Ecuador (Fig. 11). Also historically the Falla Frontal de la Cordillera Oriental between 1 and 2° N, has This work is part of my thesis to opt to the M.Sc. degree at Geol- presented several MS ≥ 6,0 earthquakes that have affected mainly ogy in the Departamento de Geociencias of Universidad Nacional the Colombia and Ecuador frontier region. The RFS presents in de Colombia. The author thanks in a very special way to the pro- this region a higher shallow seismic activity that to north of the fessors Carlos Alberto Vargas – Jiménez (director of this inves- 3° N, being observed 40 earthquakes with MS ≥ 4,5 in 450 years tigation) and Andreas Kammer. The author also thanks to other of historical data and more recent important event was March 31 professors and postgraduate degree partners of Departamento de 1983 earthquake that affected to Popayán city. Geociencias of Universidad Nacional de Colombia at Bogotá. Equally to several geologists and geophysical of the Ingeominas CONCLUSIONS in particular the regional offi ces of Bogotá and Popayán, and many independent anonymous geologists that in an or another way have The modeling applied on this investigation starting from petroge- worked with the RFS. netic and geodynamic evolution of the lithospheres that constitute the RFS at the present time in western border of the northwestern corner of South America shows that the RFS originates initially as a product of a derived continental margin of North and South 61 Germán Chicangana

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